Move repo and redirect forks

When a repository is forked, it may end up having lots of dependent repositories. If ownership is transferred (e.g. tortoisehg-stable moves from tksoh to steve), it would be nice if the repository and forks could move as well.

All forks should be updated to point to the new location of the repository.

Just adding commit permission allows multiple persons to commit, but moving a repository signals that ownership has been transferred, which is not the same.